Further observations in lincomycin-induced cholelithiasis in guinea-pigs

Lincomycin treatment of guinea pigs causes formation of pigmented phosphate containing gallbladder sludge and stones

We studied the mechanism of gallbladder sludge formation in guinea pigs (n = 30) treated with lincomycin (80 mg/kg/day) for 7 consecutive days. At sacrifice (day 8) gallbladders of treated animals contained turbid bile, sludge and in one animal a single gallstone. The precipitates were amorphous on X-ray diffraction. Infra-red spectroscopy revealed calcium phosphate as the major component. Compared to saline-treated controls (n = 15) concentrations of total protein, total phosphate and total bilirubin in gallbladder bile were significantly increased (P less than 0.05). The increase in total phosphate was due to the inorganic component, since phospholipid phosphorus was unchanged. The relative amounts of unconjugated bilirubin and of bilirubin mono- and diconjugates in gallbladder bile were unaffected by treatment as was beta-glucuronidase activity. However, sludge was enriched in unconjugated bilirubin compared to gallbladder bile. This was most probably caused by alkaline hydrolysis of bilirubin monoconjugates. To some extent, disproportionation of bilirubin monoconjugates in bile or sludge, either in vivo or during sample preparation, might also have led to increased unconjugated pigment.

Mucus hypersecretion in the gallbladder epithelium of ground squirrels fed a lithogenic diet for the induction of cholesterol gallstones

This study identified mucus granules, determined mode of release and quantified their volume in the gallbladder epithelium of Richardson's ground squirrels (Spermophilus richardsonii) fed a lithogenic diet of 2% cholesterol to experimentally induce gallstone formation. Tissue was examined using light microscopy histochemistry, scanning and transmission electron microscopy, as well as autoradiography and morphometry at the electron microscopic level. Autoradiography demonstrated incorporation of a glycoprotein precursor, [3H]galactose, within the membrane-bound granules localized in the supranuclear region of the epithelial cells. Exocytosis of granule contents was by merocrine secretion. Morphometry indicated a significant increase in the amount of intracellular mucin granules as early as 18 hr on the lithogenic diet, a feature that continued throughout the experimental period of 20 weeks. Mucus synthesis/secretion rates returned to control values within 3 weeks after removal from the diet. Scanning electron microscopy observations revealed a thick sludge-like layer overlying the epithelium at a time in the chronology of the cholelithiasic model that correlated well with the initial phases of stone formation. Histochemistry showed this layer to be a mixture of acidic mucins. Neutral mucins were not observed. The hypersecretion of mucus and formation of this sludge-like layer appear to be critical nucleating factors in the formation of cholesterol gallstones.

Nature and composition of biliary sludge

To study the microscopic and biochemical composition of biliary sludge, we subjected hepatic and gallbladder bile samples to microscopic examination, and analysis of lipids and mucus glycoprotein. These were compared with samples of hepatic and gallbladder bile obtained from normal persons and patients with gallstones. Biliary sludge was found to be sediment composed of cholesterol monohydrate crystals and bilirubin granules embedded in a matrix of mucus gel. There was a striking increase in the amount of mucus glycoprotein in the gallbladder bile of the sludge group compared with the gallstone and control group. The gallbladder biliary mucus content was also higher in the gallstone group compared with normal controls. These differences in mucus concentrations were not observed in hepatic bile samples from the three groups, suggesting that they had occurred within the gallbladder. In addition, gallbladder histology and epithelial mucin histochemical staining reaction were studied. Mucus hypersecretion and early glandular metaplasia in the epithelium were observed in the gallbladders harboring sludge, whereas those having stones had further changes in the mesenchymal tissues, with thickening and fibrosis. These results indicate that in patients with sludge the gallbladder is abnormal, showing mucus hypersecretion and glandular metaplasia. This leads to an increase in the mucus content of gallbladder bile, which in turn may result in nucleation of cholesterol crystals and may be regarded as the embryonic stage of gallstone disease.

Toxin-induced cell membrane injury in guinea pigs given lincomycin

Guinea pigs treated with lincomycin developed colitis, acute cholecystitis and abnormalities in red blood cell morphology. The present study was designed to study the production of clostridial toxins after lincomycin treatment. Lincomycin produced abnormalities in conventional but not in germ-free guinea pigs. Clostridium difficile was cultured from cecal contents of conventional guinea pigs treated with lincomycin. Cecal filtrate from sick guinea pigs was subjected to Sepharose 4B-CL and Sephadex G-200 column chromatography, yielding a partially purified toxin. Both cecal filtrate and partially purified toxin samples contained a heat labile substance which was cytotoxic to human lung fibroblast Wl-38 cells, and which was neutralized by Clostridium sordelli antitoxin. Toxin samples given orally or intraperitoneally killed normal guinea pigs. Finally, toxin samples induced red cell membrane changes in vitro as well as producing features of acute inflammation in healthy explants of guinea pig cecum and gallbladder in organ culture. Lincomycin treated guinea pigs produced Clostridium difficile toxin(s) which in turn caused diffuse cell membrane injury.

Hypersecretion of mucus glycoprotein by the gallbladder epithelium in experimental cholelithiasis

In three models of cholelithiasis (dihydrocholesterol-fed rabbits, cholesterol-cholic acid-fed mice, and Lincomycin-treated guinea pigs), the quantity and chemical composition of gallbladder epithelial mucin have been studied using (1) a spectrum of histochemical glycoprotein stains, and (2) biochemical extraction, purification and analysis of the carbohydrate components of epithelial mucin. Despite the diverse mechanism of stone induction and difference in stone composition, a common pattern of response by the epithelial mucin was observed in all three models. There was a quantitative increase in epithelial mucus production at a time before stones were formed and this increase persisted till stones were formed. There was no difference, qualitatively, between mucus produced by normal and stone-forming gallbladders.